A. Field of Invention
The present invention relates to a skateboard-type apparatus, and in particular, to a self-propelled skateboard-type apparatus.
B. Problems in the Art
Skateboards have been around for decades. Recently there has been a resurgence of the popularity of the skateboard. Also, snowboarding has recently been developed. It uses the same or similar types of athletic movement to control its direction of travel. The user stands on the top of the board and by shifting location of the user's feet and center of gravity tilts the board to cause direction change. In the case of many skateboards, what are called skateboard trucks allow the user to control the board in this manner. Skateboard trucks are usually front and back sets of wheels having the ability to both travel over a range up and down as well as pivot around a central pivot point forward and aft. Conventional skateboards and snowboards require either user propelling force or gravity to move.
Attempts have been made to develop motorized skateboards. Many mount the engine or motor at the rear or one end of the board and utilize a transmission or differential to mechanically transmit rotary power from the motor to a wheel or wheels of a skateboard truck. While these attempts try to provide self-propulsion for the skateboard, certain issues are created. For example, usually some type of rather complex mechanical linkage is required between motor and wheel because the wheel is beneath the board, in turns the wheel on one side turns at a different speed than on the other side, and the wheel is allowed both up and down and fore and aft movement. Sometimes it requires a transmission or differential. This adds cost and complexity to the device.
Furthermore, placement of motor or batteries at one end of the board can alter the center of gravity of the board. This can effect both the performance and “feel” of the board. It can important to maintain the performance and feel the non-motorized skateboard.
Still further, driving one of the wheels of the skateboard trucks can take away from the “feel” of the skateboard in the sense that the user feels he or she is being pushed or pulled. Driving one wheel can also make it difficult to maintain a straight heading with the board, and at higher speeds can create wobble or difficulty in control or direction. Moreover, driving one wheel of the wheel truck at one end of the board would not allow any smaller turning radius for the board.
Therefore, a need has been identified in the art for an improvement to motorized skateboards having motors at one end of the board with mechanical linkage to drive one or more of the wheels of the skateboard truck of the board.
Additional attempts to motorize skateboards that differ from what was previously described have been made. One example is Karrington U.S. Pat. No. 5,927,420. It utilizes a motor at one end of the board, but by chain drive drives a separate fifth-wheel positioned in the center of the board. One embodiment shows the fifth wheel behind the rear wheel truck. Another shows it near but slightly ahead of the rear wheel truck. In either case, the motor is at the back of the board. Thus, the center of balance of the board is effected. Also, a transmission, in the form of a chain drive, is needed for driving the fifth wheel.
Schlicht U.S. Pat. No. 4,073,356 and Endo, et al. U.S. Pat. No. 5,487,441 place a driven fifth wheel towards the middle of the board between opposite skateboard trucks. The engine or battery is also positioned mid-board.
However, in Schlicht, the driven fifth wheel is rigidly but rotatably mounted to the board. It relies on a built-in flexure of the board to move the drive wheel into engagement with the ground by utilizing the weight of the user, when mounting the board, to flex the board downward. When the user is off the board, the board flexes up to a normal state and lifts the wheel from the ground. This arrangement is problematic because it relies on the material properties of the board and the weight and position of the user to attempt to engage the drive wheel with the ground to propel the skateboard. Additionally, there would be a direct transmission of forces experienced by the drive wheel to the board. Especially on non-even terrain, it may be difficult for the wheel to follow the terrain in a manner that can maintain traction with the ground so that there are no interruptions in propulsion of the board.
Endo, et al. U.S. Pat. No. 5,487,441 uses an electrical motor with a battery and motor underneath the board. However, it relies upon a transmission combination to power the driven wheel. One embodiment drives one or more of the skateboard trucks and eliminates the fifth driven wheel. Another embodiment has only a front skateboard truck and one central, but rear driven wheel. It appears the design positions the fifth driven wheel such that is would always in the same plane as the bottom of the skateboard truck wheels, and thus theoretically always in contact with the ground. However, as previously mentioned, this does not provide for any independent movement relative to the board or to the other wheels and thus may not maintain contact if there is a depression in the terrain. It may also create difficulties for traction if there are protrusions or bumps.
Therefore, despite the various attempts at motorized skateboards, there is room for improvement in the art.